A Low-Cost Pressure-Driven Filtration System for Nanofiltration Membrane Evaluation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a cost-effective pressure-driven filtration system designed for evaluating nanofiltration membranes, utilizing 3D-printed components and readily available parts for approximately €60. The system employs a stirred cross-flow design to maintain stable feed concentrations during extended filtration tests, achieving a 96.5% rejection rate for a 2000 mg L−1 MgSO4 solution under 7.6 bar pressure after 24 hours of operation. I highly recommend this paper for publication due to its innovative approach to creating an affordable and efficient filtration system that demonstrates significant potential for practical applications in membrane technology. To revise this manuscript, I provide some comments for the authors.

 

1. What considerations were taken into account when selecting PETG as the filament for 3D printing the filtration system components, and how does it compare to other materials like PLA or ABS in terms of chemical resistance and structural integrity? The reason could be provided in the section of introduction.
2. Given that the system operates at pressures up to 7.6 bar, what design features ensure the structural integrity and safety of the 3D-printed components under high-pressure conditions?
3. How does the observed rejection rate of 96.5% for MgSO4 compare with other established membrane filtration systems, and what factors might contribute to the deviation from the expected 99.5% rejection rate?
4. In what ways could the flow control mechanisms be enhanced to improve the consistency of permeate recovery rates during prolonged filtration experiments?
5. What potential modifications would be necessary to adapt this low-cost system for larger-scale applications, particularly in industrial settings where higher throughput is required?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This article describes a low-cost, pressure-driven filtration system for nanofiltration membrane evaluation.

To improve the manuscript, the authors should consider these revisions:

(1) In the “2.3.  The authors should explain why they used polyethylene terephthalate glycol (PETG) filament in the "Filter Cell" section. It is noted that, in general, steel, brass, copper, etc., metals are used for the housing of the cell.  Nowadays, plexiglass, poly(methyl methacrylate) (PMMA), is used for housing cells for transparent thermoplastic.  The authors should discuss the advantages and disadvantages of filter cell housing selection and the cost analysis of the filter cell.

(2) The authors presented the cross-sectional exploded views of: (A) Dead-end cell and (B) Cross-flow cell with components labeled in Figure 1. They should include a “Stirring bar assembly” in the (A) Dead-end cell setup.

(3) The authors provided (A) a tubing diagram for the filtration system and (B) a cross-sectional exploded view of the filter cell assembly in Figure 4. It is suggested that the authors include the hollow-fiber filter setup along with the flat-sheet filter setup.

(4) In the “4.1.  In the "Membrane Installation" section, the authors should explain why they used a PTFE membrane, which has small pores. It should be noted that materials, like polysulfone (PSf), polyether sulfone (PES), polyvinylidene fluoride (PVDF), and others, are typically utilized in biotechnology and wastewater treatment processes. The authors ought to discuss the advantages and disadvantages of choosing a membrane installation, as well as how much it will cost.

The manuscript offers valuable scientific insights, and the experimental data support the conclusions. However, it requires major revisions before acceptance in Hardware in its current form. I hope the authors find these comments helpful.

Comments on the Quality of English Language

Abstract: With the growing interest in fabricating nanofiltration membranes using novel materials and techniques, there is an increasing need to evaluate the practical viability of innovative membranes at the early stages of development. In many materials research laboratories, access to professionally manufactured membrane evaluation systems may be limited. Here, we present a pressure-driven filtration system design for evaluating nanofiltration membranes that can be constructed from 3D-printed parts and widely available off-the-shelf components, at a cost of approximately € 60. The system employs a stirred cross-flow design that enables the circulation of the feed solution at the membrane surface, thereby maintaining a stable feed concentration during extended filtration experiments, similar to conventional cross-flow cells. It is suitable for the filtration of aqueous solutions containing dyes, inorganic salts, and dilute acids. Validation was performed by filtering a 2000 mg L⁻¹ MgSO₄ solution through a Veolia RL membrane at 7.6 bar, achieving a 96.5% rejection rate and a permeance of 7.5 L m⁻² h⁻¹ bar⁻¹ after 24 hours of continuous operation.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript was revised carefully and greatly improved according to the reviewer’s suggestions. The revised submission expresses the scientific insights well. The current revision is recommended for publication in the Hardware.